Scenario Engine
Compare mortgage scenarios side by side. Change the home price, rate and term, then toggle the down-payment scenarios you want to weigh. Every figure below is computed by the same verified amortization engine used across TruePITI — monthly payment, cash required at closing, mortgage insurance, lifetime interest, total cost and break-even.
This tool reports data. It does not tell you which scenario is “best” — that depends on your cash, your goals and your risk tolerance, which we cannot see.
| Scenario | Cash required | Loan amount | P&I / mo | Mortgage ins. / mo | Total / mo | Lifetime interest | Lifetime mort. ins. | PMI drops |
|---|---|---|---|---|---|---|---|---|
| 20% down | $115,000 | $400,000 | $2,584 | — | $3,192 | $530,156 | — | n/a |
| 15% down | $90,000 | $425,000 | $2,745 | $177 | $3,531 | $563,290 | $8,500 | yr 5 |
| 10% down | $65,000 | $450,000 | $2,907 | $281 | $3,796 | $596,425 | $27,000 | yr 9 |
| 5% down | $40,000 | $475,000 | $3,068 | $396 | $4,072 | $629,560 | $47,500 | yr 11 |
Rate assumption: the value you entered. Benchmark 30-year fixed 6.71% default reflects the Freddie Mac PMMS national average (2026-09-03). Data source: Freddie Mac PMMS. Calculated: 2026-09-21. Your quoted rate and costs depend on credit score, LTV, lender and points — verify before deciding.
How a scenario is calculated
- • Loan amount = home price − down payment.
- • P&I = standard fixed-rate amortization on the loan amount.
- • Mortgage insurance = conventional PMI by LTV band, charged until the balance reaches 80% of the original price.
- • Total / mo = principal + interest + property tax + insurance + mortgage insurance.
- • Cash required = down payment + an estimated 3% of price for closing costs.
Go deeper
- Mortgage calculator (PITI) — full payment breakdown
- Rate Sensitivity Engine — cost across a rate ladder
- Closing costs calculator — cash-to-close detail
- PMI calculator — when mortgage insurance drops
- Affordability calculator — what price fits your income
Methodology & Assumptions
How this calculator works, what it assumes, and where it falls short. Every calculator on TruePITI documents its math.
Formula
- P&I = L · r(1+r)^n / [(1+r)^n − 1], where L = loan amount, r = annual rate / 12, n = term months. Total monthly cost then adds property tax, insurance and (under 20% down) mortgage insurance.
Assumptions
- Fixed-rate fully-amortized loan. Rates are annual nominal; the default 6.71% is the Freddie Mac PMMS national 30-year average (2026-09-03).
- Property tax and insurance are entered as annual % of price and $/month; they do not amortize.
- Mortgage insurance uses conventional PMI tiers (good-credit band) and stops at 80% LTV. FHA/VA/USDA terms differ.
- Cash required uses a 3% closing-cost estimate — see the closing-costs calculator for a full breakdown.
Limitations
- Does not model ARM rate resets, points/buydowns, or seller-paid closing costs.
- Closing costs and insurance are estimates, not quotes from your lender.
- Mortgage insurance varies by credit score and insurer — the tier shown is one band.
Sources
- Freddie Mac Primary Mortgage Market Survey (PMMS) rate benchmark
- CFPB — Owning a home / mortgage payment definitions
Last updated: 2026-09-21. Estimates only — verify rates and costs with your lender before deciding.